1. Field of the Invention
The invention relates to engine control systems, and in particular to engine control systems for controlling the fueling system in a combustion engine.
2. Description of the Related Art
Engine control systems for controlling fueling in combustion engines often utilize fuel maps, such as shown in FIG. 1, which define the amount of fuel to be supplied for an engine operating condition. In FIG. 1, the bold line 100a represents the rated power (i.e., brake power) of the engine, and the contoured wave lines 100b represent the amount of fuel metered per horsepower (lbs/hp/hr). The curves 100a-100b are graphed against engine speed in revolutions per minute (RPS).
In a typical engine, the lowest fuel consumption occurs at point A. This is the optimum operation point for the engine under heavy engine load conditions. As can be seen, the contour lines below point A have increased fueling requirements. However, if engine load conditions are light, then the optimum operating point is point B. The difference between point A and point B can be upwards of an eight percent difference in fuel economy and is further illustrated by example below.
Until recently, software and hardware technology were not capable of adjusting fuel flow based upon actual operating conditions. Fixed point operation was necessary, either point A or point B or some other fixed point, with the inherent trade offs in performance under all other operating conditions. Engines offered in the industry are currently available optimized at either point A or point B. Point A configured engines perform best under heavy load, but poorly when lightly loaded. Point B configured engines perform best when lightly loaded, but have poor fuel consumptions when heavily loaded. Such, fuel maps are often optimized for different operating conditions.
Engine parameters (e.g., A/F ratio, amount of fuel, etc.) currently are set for average conditions under which they operate. In other words, the engine is optimized for the average conditions that are predicted for its service and not for actual usage. This leads to compromises in engine fuel efficiency. The tendency is to optimize the engine to work at or near full load, which is represented by the published engine horsepower and torque curves. See FIG. 2.
Operation around the full load line represents operating conditions such as heavy acceleration, high payload or traversing steep grades. However, conditions exist where light engine loads are encountered, such as some vehicle operations under less than full cargo, at low cruising speeds, or flat or downhill road grades. Under these conditions, fuel is wasted because the best operating point in the engine is not at the conditions the vehicle is experiencing. For example, the Mack® E7 ASET engine is optimized for operation at close to 100% load. Other engines, available in the Heavy Duty industry, may be optimized for partial load operation, such as when the vehicle is pulling less than a truckload of freight.
An engine using a fuel map that is optimized for 100% load operation may deliver better fuel economy under demanding conditions, such a mountainous terrain, than an engine using a fuel map optimized for partial load operation. Conversely, using a fuel map optimized for partial load operation may deliver better fuel economy over flat terrain than one would using a fuel map optimized for 100% load operation. The probability that an engine developed for one set of operating conditions would be mis-applied to another set of operating conditions, however, is high.
Fuel economy tests were run for two similar trucks under mountainous and flat operating conditions that illustrate this point. The first truck was a Mack® CH outfitted with an E7 engine optimized for 100% load operation, and the second truck was a competitor outfitted with a competitor engine optimized for partial load operation. In a first test, the Mack® and the competitor were operational under identical operating conditions on a mountainous route from Richmond, Va. to Lexington, Ky. along U.S. Interstate 64. During this test, the Mack® achieved 6.5 miles per gallon (mpg) while the competitor achieved 6.27 mpg—3.5% lower fuel consumption than the Mack®.
In a second test, the Mack® and the competitor were operational under identical operating conditions on a flat route from Richmond, Va. to Atlanta Ga. along U.S. Interstate 95. The engines of each of the trucks were running at partial load during this test, outputting only approximately 150 horse power (hp) out of a maximum rated output of 350 hp. During this test, the Mack® achieved 6.95 miles per gallon (mpg) while the competitor achieved 7.32 mpg—5.3% higher fuel economy than the Mack®.
As can be clearly seen from the experiment, the first and second trucks respectively out performed each other in the first and second tests. Thus, there is a need for improved engine control that does not depend upon a single fuel map or is not optimized for a single set of operating conditions.